Electrical precipitator



March 5, 194%.

H. J. WHITE ELECTRICAL PRECIPITATOR Filed Dec. 10, 1945 I 4 Sheets-Sheetl Patented Mar. 5, 1946' UNITED STATE PATE NT orrice I ELECTRICALPRECIPITATOR Harry J. White, Cambridge, Mass, assignor, by

direct and mesneassignments, of one-half to Research Corporation, NewYork, N. Y.-, a corporation of New York, and one-half to WesternPrecipitation Corporation, Los Angeles, Calif a corporation ofCalifornia Application December 10, 1943, Serial No. 513,765

3 Claims. (0]. 183-7) -mon practice to effect charging of the suspendedparticles by passing them between two opposed electrodes between which ahigh potential differe'nce is maintained, one of the two electrodesbeing a discharge electrode at whichthere is silent or corona electricaldischarge that ionizes the gas and causes the suspended particles tobecome charged with the same electrical sign as the discharge electrode.This is termed charging action.

In the "single stage type of precipitator, the charged particles migrateunder the influence of the electric field between the electrodes towardthe other electrode which is a non-discharge electrode of extendedsurface, and collect or become precipitated upon the surface of thatelectrode Zvhich is consequently termed the collecting elecrode.

passes into a second or precipitating field, typically .maintainedbetween opposed non discharged electrodes, and, under the influence ofthemecipitating field, the charged particles migrate to one of theelectrodes between which the field is maintained and are depositedthereon. The latter electrode is likewise termed a collecting electrode.The novel collecting electrode structures of the present invention maybe advantageously utilized as collecting electrodes in eithersinglestage or two-stage precipitators.

In the following description and in the ap pended claims, the termdischarge electrode will be understood to designate an electrode thatfacilitates corona discharge therefrom, because it has a configurationthat establishes a sufflciently high potential gradient at or near itssurface to create corona discharge before there is a disruptivedischarge or spark-over. For this purpose the discharge electrodeusually takes the form or a a member of small surfacearea, such as asmall or points, whereby they may be created in the immediate vicinitythereof a sufllciently high electric field intensity to causeionizationand corona discharge. .The term "non-discharge electrode" willbe understood to designatean electrode that minimizes or prevents coronadischarge therefrom because it has a configuration that establishes asufllciently low field concentration at or near the surface tosuppresscorona discharge at elevated potentials lower'than the voltage requiredfor disruptive discharge or spark-over. For this purpose, anon-discharge electrode usually is one of extended surface area,substantially free from harp corners or other parts of sharp surfacecurvature at all portions which are located within the electric field,so as to substantially avoid ionization or'corona discharge at thatelectrode.

Dust'particles in the gas stream become elec- I trically charged in theionizing field and there In the two-stage or "separated field v type ofprecipitators, the gas containing-all or a substantial proportion of thecharged particles migrate to the collecting electrode under the infiuence or the electrical forces exerted on them, and when the particlesreach and are precipitated on the electrode the electric charges areneutralized or lost. The layer of dust particles on the electrode is expsed ordinarily to the gas stream which tends to blow off looseindividual particles or agglomerations'of particles, the erosion being aresult of the gas velocity. The par ticles are held on the electrodemore or less securely against erosion either by electrical forces or bythe physical properties of the particles themselves. When the collectingelectrode is within the range of'the charging field, as in the singlefield type of precipitator, the field recharges and reprecipitates mostof the particles that may be blown oil the electrode, but even then someparelectrode or toeach other.

ticles are blown along the electrode surface and of! the outlet end ofthe electrode when the dust has such physical properties that theparticles offer little resistance to gas erosion. In the twostage typeof precipitator' in which there is typically no corona discharge in thesecond or precipitating field, most of the material removed from thecollectingelectrode by erosion is not recharged and is carried out ofthe precipitator by the gases. There are some dusts being fiy ash"which. is composed of particles that have a generally spherical shapeand have very little inherent tendency to adhere to the Characteristicssuch as these facilitate erosion of the precipitated dust that areparticularly hard to collect for this reason, one typical examplecleaned gases. Very little erosion takes place at low gas velocities andmay be neglected, though the rate increases slowly with increasingvelocity .up to some velocity termed the "critical velocity above whicherosion loss increases rapidly with an increase in velocity and becomesquite appreciable. It is probably true of most dusts, if not all, thatthere is a critical velocity above which losses are appreciable. Thepresent interest centers particularly around dusts for which thecrittained.

This collection difflculty is inherent in the nature of the dust beingcollected and has the eifect of reducing the capacity of a unit of agiven size operating at a given normal efliciency. because of thelimitation on dimensions required in order to keep the gas velocitybelow critical values. Expressed differently, the reduction incollection efficiency caused by erosion losses ini be provided at leastin part by the extended surcreases the size of the plant and equipmentrequired to treat a given volume of gas without falling below a minimumeiflciency.

A principal object of the invention is to provide an improved electricprecipitator in which loss of collected material by erosion orredispersion in thegas stream is substantially reduced or eliminated.

A further object of the invention is the -provision'of an improved formof collecting electrode construction for electrical precipitators.

, Another object of the invention is the provision of an improved methodfor the removal of susaegded particles from gases by electrical precipi-These and other objects and advantages which will be clearly apparentfrom the following description of the invention are attained by theprovision of a collecting electrode structure inface memberswhichprovide the primary material collecting surfaces, utilizing, forexample, opposite faces of said members to provide the two collectingsurfaces. When the secondary material collecting surfaces are providedby different members from those providing the primary materialcollecting surfaces, the latter members may also provide or support theprecipitating electrode members which cooperate with the secondarycolture will typically be of the non-discharge type.

In general, the average field strength between the precipitatingelectrode members within the vertical passageways and the secondarycollecting surfaces therein may be of the same order as theaverage fieldstrength between the collecting electrode structure and theprecipitating electrode members complementary thereto.

The invention will be more particularly described for the purpose ofillustration with reference to the accompanying drawings in which:

F18. 1 is a sectional elevation of an electrical precipitator embodyingthe principles of the invention;

Fi 2 is a partial plan view of the precipitator of Fig. 1 with the topcover plate removed;

Fig. 3 is a partial sectional elevation on line H of Fig. 2, and

,l igs. 4 to 8 are diagrammatic representations of illustrativeembodiments of the invention.

eluding primary material collecting surfaces at least partially exposedto the stream of gas being treated, secondary collecting surfaces fullyY shielded from the stream of gas, precipitating electrode meanspositioned to precipitate material on said secondary collectingsurfaces, and mean for directing a flow of gas including material erodedfrom the primary collecting surfaces into the space between thedischarge electrode means 6 and the secondary collecting surfaces.

A typical electrical precipitator embodyin the invention includes aprecipitating electrode structure and a collecting electrode structurespaced therefrom to define a gas passage therebetween and comprisingextended surface members defining one or. more vertically-extendingpassageways f and providing primary material collecting sur- .faces anda plurality of openin s, preferably verments or suitably positionedfans, for directing as, flow from said gas passage into saidvertipassageways. means providing secondary Wu! collecting surfaceswithin the passageways, and'precipitating electrode members; within theverticallyextending passageways spaced and insulated from the secondarymaterial collecting surfaces.

In Figs. 1-3, I! is; a precipitator casing provided with gas inlet ii,gas outlet i2 and a collecting hopper it for precipitated material.

Within the casing iii are complementary precipitating and collectingelectrode structures spaced apart to define longitudinal gas passagesthrough the casing.

The precipitating electrode structure comprise discharge electrodes i4,consisting of wires suspended from horizontal tubes I! and maintainedtaut and in proper spaced relationship by rods ii. Tubes II are carriedon I-members I! which are supported on insulators l8 and insulatorbushing it contained in insulator housings It. The precipitatingelectrode structure is 5 energized through the insulator bushing IS.

The collecting electrode structure comprises a plurality of sheet metalmembers-2|, shaped and rranged to provide a plurality ofvertically-extending passageways 22 having vertical inlet slots 22c andoutlet slots 22b. Adjacent the inlet slots 22a the members II areprovided with lip member Ila, extending outwardly into the gas pas-'Within'each of the vertical passageways 22 provided by members 2!, ispositioned a'discharse electrode 14 suspended from horizontal tubes 25and maintained tent and in proper position by rods fl. Tubes 28 arecarried on I-members 21 The secondary material collecting Q which 7 aresupported from insulators 2| and in.

ascaesr sulating bushing 29 through which the discharge erosion. Thusthe whole or a major part of the deposited material is carried along theprimary collecting surface in the direction of gas flow in'the main gaspassages. The lips 2 la projecting from the collecting surfaces adjacentthe inlet slots 22a cause a small portion of the gas stream adjacent thecollecting surfaces to flow into each of the passageways 22, acorresponding amount of gas flowing out of the passageways throughoutlets 22b. The amount of flow through the passageprimary collectingelectrode surfaces at ground potential with the primary precipitatingelectrodes being of negative polarity with respect to ground potential,and the secondary precipitating electrodes also being of negativepolarity with respect to ground potential in the forms of the ing theangle of the lips Ma or by any combination of these means, and ispreferably adjusted to a velocity which will permit a high efliciency ofprecipitation within the passageways;

Thus the material deposited in the primary precipitating field istransferred by erosion and gas flow into a secondary precipitating fieldwhere it is collected under conditions of relatively low gas velocityupon the shielded innersurfaces of members 2|. Very high gas velocitiesof. 25 to 50 1 feet per second or even higher may be used in g the maingas passages.

Th collecting electrode structures may be rapped during operation tocause the collected material to drop into a hopper or other suitablereceiver in the bottom of the apparatus.

Alternative arrangements and constructions of the inlet andoutlet'openings and the lip members are shown diagrammatically in Figs.4, 5 and 6 in which corresponding elements are given the. I same numberas in Figs. 1-3.

In the construction of Fig. 4, the primary precipitating electrodes H"are shown as nondischarge electrode members, while'in the constructionof Fig. 5 the secondary precipitating electrodes 24' are shown asnon-discharge electrode members. charge type primary and secondaryprecipitating electrodes shown in the constructions of Figs. 1 to 7 mayalso be made. The use of non-discharge type primary precipitatingelectrodes, as shown in Fig. 4, together with either'dischargeornondischarge type secondary precipitating electrode members, isparticularly advantageous when using the construction as the second orprecipitating stage of two-stage electrical precipitators.

Similar replacement of the dis- In general, it is preferable to maintaina potential difference between the primary precipitating electrodes andthe collecting electrode structure at about 30 to kv. with a spacing of4 inches,

for example, if th primary precipitating elec trode. is. of thedischarge type, and somewhat higher, say 40m kv. for the same spacing,if

' the precipitating electrode is of the non-discharge type. Averagefield strengths of the same order of magnitude are preferably maintainedbetween the secondary precipitating electrodes and the invention shownin Figs. 1, 2, 3, 4, 6 and 7, and being of positive polarity withrespect to ground in the form of the invention shown in Fig. 5. In

as the general potential difference relations sug-' gested above aremaintained.

In the arrangement shown in Fig. 7, the gas passageways 22 have aplurality of inlets 22a and a single outlet 22b which may be leddirectly into the gas stream or may be connected to a suitable system ofducts leading to an exhaust fan, as

indicated in the drawings, to provide a more positive control of the gasvelocity through the secondary collecting spaces 22. Instead of'the ductsystem, adjustable dampers, such as are shown in- Fig. 8, may beprovided-at the outlets 22b.

In the form of the invention shown in Figs. 8 and 9, the dischargeelectrode elements llla providing the secondary precipitating coronadischarge are carried by extended surface members 40, which provide theprimary material collecting surfaces, and-the secondary materialcollecting surfaces are provided by extendedsurface members 4 l whichare insulated from the members I. The members 40 define ,gas passageways42 witninlet openings 42a and outlets 42b. The outlets 42b may beprovided with adjustable dampers 43, as shown, or may be connected to asuitable flue and fan system as indicated in Fig. I.

The discharge precipitating electrodes H of Fig. 8 may. be replaced bynon-discharge type precipitatingelectrodes as shown in Fig. 4 and thedischarge elements 40a may be eliminated from extended surface members40, so that the latter act as non-discharge precipitating electrodeswith respect to secondary collecting electrode members ll.

I claim:

1. An electrical precipitator comprising: a primary precipitatingelectrode structure;a collecting electrode structure spaced therefrom toprovide a gas passage therebetween and comprising wall means defining avertically extending space within said collecting electrode structureand shielded from the flow of gas in said passage, said wall meansproviding primary material collecting surface portions of extended areafacing toward said gas passage, secondary material collecting surfaceportions of extended area facing toward said shielded space, and aplurality of slots establishing communication between said gas passageand said shielded space, said slots being spaced apart in the directionof gas flow in said passage and extending. transversely with respect tosaid gas flow, and said collecting electrode structure being providedwith gas deflecting members disposed adjacent said slots in position todirect gas from said gas passage into said shielded space and withatleast one opening for outflow of gas from said shielded space at aposition removed from said slots; and secondary precipitating electrodemembers within said shielded-space and spaced from said secondarymaterial collecting surface portions. v

2. Anelectrical precipitator comprising: a priprecipitating electrodestructure: a collect-v electrode'structure spaced therefrom to provide agas e therebetween and comprising wall means defining a verticallyextending space withinfisaid collecting electrode structure and shieldedfrom the flow of gas in said passage, said wall means providing-primarymaterial collecting portions of extended area facing toward said a: e, Vsecondary material collecting portionso'tjexte'nded area lacing towardsaid shieldedspace, a plurality or slots establishing'comniunicationbetween saidgas e and *said shieldedspaca'saidmlots being spaced apartlnthe direction or gas flow in said passage and eitending transverselywith respect tosaid gas assess-z 3. An electrical preeipitatorcomprising: a primary precipitating electrode structure; a collectingelectrode structure spaced therefrom to provide a horizontally extendinggas passage therebetween and comprising wall means defining a pluralityof vertically extending passageways within said collecting electrodestructure and shielded from the flow of gas in said passage. said wallmeans providing primary material collectiiow,' and said collectingelectrode structure being I provided 'withgas deflecting membersdisposed ing surface portions of extended area facing toward said gaspassage, secondary material collecting surface portions of extended areafacing toward the. respective shielded passageways, and a pluralityof'horizontally spaced vertical slots establishing communication betweensaid gas passage and the respective shielded passageways,

and said collecting electrode structure being provided with gasdeflecting members disposed adjacent said slots in position to directgas from said gas passage into said shielded passageways and withopenings for outflow of gas from the respective shielded passageways atpositions removed from said slots; and secondary precipitat- .ingelectrode members within. the respective shielded passageways and spacedirom said secondary material collecting surface portions.

